Reading scores on the SAT for the high school class of 2012 reached a four-decade low, putting a punctuation mark on a gradual decline in the ability of college-bound teens to read passages and answer questions about sentence structure, vocabulary and meaning on the college entrance exam.

Many experts attribute the continued decline to record numbers of students taking the test, including about one-quarter from low-income backgrounds. There are many factors that can affect how well a student scores on the SAT, but few are as strongly correlated as family income.

Scores among every racial group except for those of Asian descent declined from 2006 levels. A majority of test takers — 57 percent — did not score high enough to indicate likely success in college, according to the College Board, the organization that administers the test.

In the Washington region, average statewide reading scores in Maryland, Virginia and the District all slipped slightly from 2011. But in Montgomery, Fairfax and Arlington counties, students outperformed their peers across their states and the country. And Montgomery County set a record for total average scores.

But the national trend lines are alarming and should serve as “a call to action,” College Board President Gaston Caperton said. “When less than half of kids who want to go to college are prepared to do so, that system is failing.”

The nearly four-hour SAT covers critical reading, writing and math. Each subject is worth a maximum of 800 points, for a potential total of 2400 points. For generations, SAT scores have been used, in conjunction with grade-point averages, by college admission officers to judge whether an applicant is likely to succeed at their school.

But questions about whether the SAT is biased in favor of middle-class and wealthy students have led many colleges and universities to use other gauges or to accept an alternative exam, the ACT, which edged out the SAT in 2012 for the first time as the nation’s most popular college entrance exam.

There is a significant correlation between family income and test scores on the SAT, with average scores increasing with every $20,000 in additional family income.

Educational experts are divided over the causes. Some assert that privileged students do better on the SAT because they are exposed to activities, from summer camp to private violin lessons, that give them an advantage in that particular test. Others point to the fact that affluent parents can provide private tutoring and privileged students can afford to take the test multiple times.

Still, many school districts — and parents — traditionally have seen SAT scores as an important measure of the quality of a K-12 education.

Across the country, 1.66 million seniors who graduated last June took the SAT, the highest number since the exam was first administered in 1926 to a few thousand overwhelmingly white and privileged students headed for Ivy League schools. In many places around the country, school administrators have been nudging more students to take the exam, saying that all students should consider college. In Prince George’s County, officials plan to offer the exam during the regular school day this year, making it more convenient for students.

The average reading score for the 2012 graduating class was 496, down one point from the previous year and 34 points since 1972. The average score on the writing portion of the exam was 488, down nine points since that subject was first tested in 2006. Math scores were flat, compared with 2011.

More than a quarter of students in public schools who took the test — 27 percent — came from families with income low enough to qualify for a waiver of the $50 test fee. More than a third of all test takers reported that their parents had not attended college.

The 2012 SAT scores come after a decade of efforts to raise test scores under the No Child Left Behind law, the federal education initiative crafted by President George W. Bush. Critics say the law failed to address the barriers faced by many test takers.

“Some kids are coming to school hungry, some without the health care they need, without the vocabulary that middle-class kids come to school with, even in kindergarten,” said Helen F. Ladd, a professor of public policy and economics at Duke University.

“If we really want to do something to close achievement gaps and raise test scores, we have to stop putting our heads in the sand and start addressing this issue,” she said.

As a way to better prepare high school graduates for college or careers, 45 states and the District of Columbia are planning to implement common academic standards over the next two years. Among other things, the new standards are designed to better teach reading comprehension and critical thinking.

In the Washington region, Montgomery County students posted an average combined score of 1651, or 14 points higher than graduates the year before. That was 184 points higher than the statewide average and 153 points higher than the national average.

In Fairfax County, students made modest gains, posting an average total score of 1659, up five points from a year earlier.

In the District, students in public schools scored an average of 1184, nearly 300 points below the national average.

In Prince George’s County, the average SAT score dropped eight points, to 1274. Reading scores fell two points; math dipped two points; and writing dropped four points.

In Arlington County, the average score rose 14 points from 2011, to 1641. There were significant gains among black and Hispanic students, although their average scores continued to lag those of white and Asian students.

Scores in Prince William County public schools stayed flat at 1490, with reading up a point but math down a point and writing staying the same.

Alexandria City Schools scores increased from the year before but remained below state and national averages. In a district that is about 40 percent black, 30 percent Latino and 28 percent white, “when I hear that 65 percent of our seniors took the SATs last year, that’s great news,” Superintendent Morton Sherman said.

In Loudoun County, test takers averaged 1590, down two points from 2011.

Montgomery County School Superintendent Joshua Starr said his district was able to set a record through a combination of practices, such as early childhood education and analyzing data to make specific systemwide improvements.

“I don’t want people to think there is simply one program or initiative or a silver bullet,” said Starr, who is a vocal critic of No Child Left Behind and other recent education policies such as the Obama administration’s Race to the Top. “It’s really a holistic approach.”

African American and Hispanic students from Montgomery County made gains on the SAT this year, outperforming their peers nationwide. African American graduates earned a combined score of 1389 on the SAT, up seven points from the prior year, while scores for Hispanic students rose six points, for a combined score of 1483.

Still, Starr said there were stubborn differences in participation and performance along racial and ethnic lines. “There are some persistent gaps and we have to make sure we have to address those,” he said.

The Washington area had some of the higher test-taking rates in the nation.

Only five states had a higher percentage of test takers than the District, where 83 percent of public- and private-school seniors took the SAT. Meanwhile, 74 percent of Maryland seniors and 72 percent of Virginia seniors sat for the exam.

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